Electronic locating systems

ABSTRACT

Methods and apparatus are disclosed for location of objects to facilitate retrieval, filing, security, inventory stock-keeping and the like. The methods and apparatus employ a tag element associated with each object-to-be-located, and interrogation system for searching one or more spatial regions for such tagged items, as well as mechanisms for identifying objects within the interrogated region.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/562,247, filed May 2, 2000, now U.S. Pat. No. 6,388,569, which is acontinuation of U.S. patent application Ser. No. 09/134,790, filed Aug.14, 1998, now U.S. Pat. No. 6,057,756, which is a continuation of U.S.patent application Ser. No. 08/478,866, filed Jun. 7, 1995, now U.S.Pat. No. 5,798,693.

BACKGROUND OF THE INVENTION

The technical field of this invention is electronic communicationsystems and, in particular, systems for locating and/or retrievingobjects by electromagnetic interrogation of a spatial region to detectthe presence (or absence) of an object.

Searching for possessions, tools and other objects is often atime-consuming task. Since the beginning of history, people have soughtto solve this problem in many ways by devising implements to help keeptrack of useful objects. For example, one of the earliest metalimplements devised by man was the bell, used by shepherds and otherhandlers of animals to locate their flocks or herds. As civilization hasdeveloped, so has the need for locating and identifying useful objectsor possessions. Modern society faces an unparalleled proliferation ofpersonal and business objects, many of which are either visuallyindistinguishable from each other or are difficult to examine readily.Examples of such objects include office files, business inventory,retail merchandise, luggage, freight and other commercial or personalitems.

Office files are a particularly perplexing problem since it is commonfor more than one individual to work on a file, e.g., to add papers,make notations or otherwise review and/or revise the file's contents.Office productivity is lost whenever a file is misplaced or can not belocated. Accuracy and efficiency are also lost whenever papers can notbe placed into an appropriate file in a timely fashion.

Another area where tracking of objects is of critical importance is inshipping, where packages destined for diverse locations must be storedand then routed to particular carriers or vehicles. This problem isparticularly acute in luggage handling where lost articles of luggagecan be especially vexing to passengers. At present, visual tags are usedto identify the destination of luggage. However, there is no simple wayto verify if all the luggage intended for a particular destination hasbeen loaded on the proper carrier, and it is difficult, even with visualtags, to find misplaced or misrouted items of luggage.

Similarly, the management of retail items, such as clothing, or stockparts for manufacturing purposes often requires inventory-taking. If anitem can not be located, e.g., an article of clothing in a particularsize or a manufacturing part of particular characteristics, then a saleis lost or a manufacturing order goes unfilled. Moreover, the businessmanager may order supplemental items, not knowing that a supply existson the premises in some unidentified location.

Recently, a number of electronic finding aids have been developed. Forexample, many cordless telephones now come equipped with a radioreceiver to assist in their location in event that the telephone headsetis misplaced. A transmitter incorporated into the charger/line interfacemodule emits a signal that causes the headset to ring when a button isactivated on the interface module. Similarly, the problem of lost keyscan sometimes be remedied by a key chain tag which generates an alarm inresponse to certain sonic signals, such as a sharp whistle or a loudslap.

Unfortunately, conventional electronic finding aids are not capable oftracking large inventories or large numbers of files. In many cases, thesimplicity of the finding aid system (e.g., the nature of thetransmission signal or the receiver) makes it impossible to distinguishone object from another. In other cases, the overlap of signals fromvarious sources causes too much interference when a plurality of objectsneed to be located. There exists a need for better electronic locationsystems, particularly systems that can accommodate the tracking of largenumbers of files, items of inventory or the like.

There also exists a need for systems and methods that would permitautomatic inventory-taking of files or merchandise on a regular basis(e.g. daily or on another periodic basis), as well as permit immediateor real time location and retrieval of objects in diverse environments.

Moreover, simple systems for locating and/or retrieving objects whichcan be incorporated into a conventional office or commercial dataprocessing or communications infrastructure would likewise enhanceefficiency while also achieving a cost economy as a result ofintegration with existing hardware and/or software.

SUMMARY OF THE INVENTION

Methods and apparatus are disclosed for location of objects tofacilitate retrieval, filing, inventory stock-keeping, security and thelike. The methods and apparatus employ a tag element associated witheach object to be located, and an interrogation system for searching oneor more spatial regions, as well as mechanisms for identifying objectswithin the interrogated region.

In one simple embodiment suitable, for example, for inventory controland security purposes, the tag element can be a electromagnetic antennaand/or signal receiver which responds either passively or actively toannounce the presence (or absence) of an object within a controlledregion defined by a broadcasted electromagnetic interrogation signal,e.g., a low power radio or microwave frequency electromagnetic radiation(EMR) transmission, or a time-varying magnetic field.

In one aspect of the invention, the tags can include a coding mechanismfor uniquely defining particular objects, thereby facilitating location(and retrieval, if desired) of one or more desired objects from aplurality of objects present within an interrogated region (e.g., anoffice, file room, retail floor display or stockroom). This embodimentis particularly useful, for example, in locating specific files withinan office or other workplace environment, in locating merchandise withina store, or in locating specific stock within a warehouse or stockyard.

One or more interrogation signal generators, or search beacons, can beused to search each interrogation region. The beacons can be simpleelectromagnetic field generators (e.g., radio transmitters or magneticfield coils) which merely cause a specific tag to respond, or they canbe more complex. In one preferred embodiment, the beacons can beconstructed as transceivers (or operated in conjunction with a set ofdistributed receivers) to both transmit an interrogation signal andreceive a responsive signal, echo, or otherwise sense a fieldperturbation, indicating the presence of a specific tagged item withinthe interrogation region.

Moreover, the beacons can poll the various regions for all tagged itemsand then take a census of each region's contents. When serving in acensus-taking role, the beacons can cooperate with a master controllerto report the census results and, thereby, construct a master census ofall tagged items within the controlled system. This aspect of theinvention is particularly useful in office environments, for example,where files are often moved during the course of a day. An individualseeking access to a file need only consult the master controller for thelast known location of the file. This aspect of the invention is alsouseful in keeping track of parcels, freight or baggage during transit.By conducting censuses on a periodic basis, e.g., at the beginning of aday and hourly during the course of business, the location of all taggeditems can be readily tracked.

In a further aspect of the invention, systems and methods are disclosedwhereby a user can interactively request the location of an object, anda controller can check stored census data to determine the last knownlocation of the object. The system can then interrogate the region ofthe last known location to verify that the object is still there. If theobject is found at the same location, the user is immediately notified.If the object is not found at its last census location, other regionscan be polled either globally or on a region-by-region basis to locatethe object. The user is then notified of the new location and the censusis updated either entirely or partially based on the search protocolchosen.

The tag coding mechanism can take a variety of forms. For example aresonant circuit can be employed which responds to a predefined sequenceof electromagnetic radiation, e.g., radio waves or the like, bytransmitting a responsive signal to indicate the object's presencewithin the interrogation region. The resonant circuit can take the formof a tapped delay line or tank circuit which resonates, accumulates oramplifies an electronic signal in response to a specific frequency ofradiation (or modulation pattern) in a broadcasted interrogation signal.In another embodiment, a reflecting delay line can be constructedemploying a piezoelectric reflector to receive and/or retransmitelectromagnetic radiation. In yet another embodiment, the tag elementscan incorporate a magnetic material, for example, a ferromagnetic markeror the like, which interacts with a time varying magnetic field in sucha way as to perturb the magnetic field and, thereby, announce the item'spresence within the interrogated region.

By transmitting a programmed interrogation signal which has a specificcode, e.g. a signal modulated with a particular time-varying frequencyor amplitude pattern, which matches the code of one tag element (or asubset of the tags), the present invention ensures that only one taggedobject (or only one class of tagged objects) will respond, therebypermitting a user to search for, and locate, specific objects.

The interrogation signal can be implemented by low power, safe, highfrequency radio waves, such as broadcast frequency signals in the rangeof about 10 kHz to about 1000 MHz, or similar low power, safe, microwavesignals in the range from about 1000 MHz to about 2200 MHz. Frequenciesallocated by the FCC for industrial, scientific and medical purposes,which may be useful in implementing the present invention, include the 5MHz, 13.5 MHz, 27 MHz, 40 MHz, 49 MHz, 132 MHz and 905 MHz bands. In oneembodiment, the invention can be implemented using one or more of thespecific frequencies allocated by the FCC within the 49 MHz band whichsupport and permit digitally encoded transmissions. Alternatively,digital signal transmissions within the 900 MHz band can be employed.Various other frequencies can also be employed in accordance with FCCand other regulations. The term “radio frequency” as used herein isintended to broadly encompass electromagnetic radiation at frequenciesranging from about 10⁴ Hz to about 10¹⁴ Hz, including both conventionalbroadcast and microwave signals.

Modulated magnetic fields can also be used in certain applications. Forexample, the interrogation means can generate a magnetic field of about0.01 Oersteds to about 1.0 Oersted modulated at a frequency ranging fromabout 0.1 kHz to about 100 kHz to interact with coded ferromagnetic tagelements and, thereby, indicated the presence of tagged objects withinthe interrogation region. As used herein, the term “electromagneticsignal” is intended to encompass both electromagnetic radiationtranmissions and time-varying magnetic fields.

Alternatively, the broadcast signal can be fixed waveform, e.g., aselected frequency or modulation pattern which induces differentresponses by particular tag elements, which are sensed by a receiverwhich is not associated with the tag but located within theinterrogation region, thereby allowing the user to poll-controlledpremises (or smaller spatial regions, such as individual offices,storerooms, or filerooms) in order to inventory the contents of suchpremises or regions, or to identify a particular item by itscharacteristic response. In such an embodiment, a predefined (e.g.,fixed or swept) frequency interrogation signal, for example, having afrequency ranging from 1500 to about 2500 kHz can be employed with aseries of uniquely coded resonant tag elements. In one approach, thetags are distinguishable by differences in their capacitance and/orinductance, resulting in distinctive “signatures” when they resonate inresponse to the interrogation signal. In this embodiment, a monitorsituated in each controlled spatial region recognizes each response toan interrogation signal and determines from the response (e.g., anelectromagnetic echo signal or field perturbation) that certaincontrolled objects are present (or absent). In addition to theresponsive signal which is communicated to an electronic monitor orreceiver, the tag can be constructed to emit an audible signal whichinforms nearby individuals that a search request has been initiated.

Thus, the present invention can perform as an electronic watchman inwhich a plurality of individual transceivers, or systems of transmittersand monitors, serve as beacons to generate search signals within certainregions and as monitors to receive signals back which identify thetagged objects within the interrogated zone. Distributed beacons can beactivated either or all at once or sequentially, and preferably are incommunication either with each other or with a central controller forperiodic census-taking. For example, such a system can be used toconduct a general census at the end of business (or the beginning of awork shift). Alternatively, periodic interrogations can be conductedthroughout a workday (e.g., once every hour or other predefined timeperiod) to provide an updated census of inventory, files or other taggeditems. Preferably, the system can also provide for a user-initiatedsearch at other times and thereby generate a current location censuswhenever a need for such arises.

In the context of office files, such a system represents a significantimprovement over prior art systems that rely upon eithermanually-maintained records (such as sign-out cards) or bar-code typesystems that likewise require individuals to process a file (e.g., by“wanding” it with a bar code reader) each time it is moved from onelocation to another. In the context of luggage tracking, the presentinvention represents a significant improvement in that it permitsluggage handlers to verify that all luggage in a particular lot orlocation share a common destination (or route leg) and in at least someembodiments also allows the user to determine the number of pieces in ashipment and to initiate a search for lost items. Various other workenvironments, besides offices and transportation facilities, also canbenefit from the present invention. For example, libraries wheremanagement of circulating collections is desired, or manufacturingfacilities, where work-in-progress needs to be tracked, can likewiseemploy the present invention.

In a simple embodiment, the present invention can be used in conjunctionwith conventional tracking systems, such as manual, bar-coded or“wanded” location control systems, as a mechanism for alerting usersthat an article has not been properly logged in (or logged out). Forexample, a parcel or other object which is assigned to particularlocation can be tagged with a device according to the present inventionwhich will beep or otherwise trigger an auditory signal if the articleis removed without being re-coded for a new location.

Alternatively, the tags can be constructed to remain silent so long asthey do not pass into a specific interrogation zone. Thus, a parcel orluggage item can be tagged to ensure that it does not leave the shippingdock without proper dispatch and, similarly, does not get routed to thewrong carrier or storage area. Such a system would likewise be useful incontrolling the release of merchandise from a stockroom or files from acentral filing area.

In another alternative embodiment, a predefined time delay can beestablished before the locating device is re-armed whenever it is codedfor transfer. So long as the tagged object arrives at the intendeddestination within the predefined delay period, the alarm will not beactivated. However, if the object is misplaced enroute, or delivered tothe wrong destination, the alarm will be triggered when the delay periodruns out. In yet another variation, the tag can be temporarilydeactivated for transfer without pre-coding any new destination, therebyallowing a carrier a limited period of time to deliver an object to anew location. Once the object has been delivered, it can be logged inand the alarm would be deactivated.

More generally, the present invention encompasses systems that provide asignal whenever a tagged item is found in an area where its presence hasnot been preauthorized. If the tag's alarm is triggered, a responsibleparty can return the object to an authorized location, or override thealarm, for example, by reprogramming the tag to authorize a newdestination. Such reprogramming can be performed at the originallocation (or any available intermediary waystation) or the user canproceed to the new location to log in the transfer.

In another embodiment, various users can be allowed access to thegeneral census data to determine the location of files, luggage,collections or other tagged objects. In such embodiments, the electronicwatchman functions of the invention can be integrated into (or otherwiselinked to) existing office hardware such as networked personal computers(e.g. via an electronic mail subroutine or a separate applicationprogram) or telephones to permit a user to find a file or the like byreference to the last census (or to initiate a new search for a taggedobject). Alternatively, such user interface elements can be stand-alonehardware devices which are situated in individual offices or otherlocations within the controlled region to provide ready access to thecensus and/or search facilities of the system. In either embodiment, thedistributed poll-taking elements can be employed not only to detect thepresence of a particular tagged item but also to alert nearby persons(e.g., office occupants, luggage handlers, shipping dispatchers, retailclerks or stockroom personnel) that a request has been made fordetermination of the location of the item.

While such search facilities simply can be activated by a keypad or“mouse-like” hand tool (usually in conjunction with a display screen),in another aspect of the invention, search operations can be initiatedby voice-driven speech-recognition systems. The system can also respondin an audible fashion regardless of the form in which the search isinitiated and thereby provide an inquirer with an oral report on thelocation of a file or more detailed information on its status (such asfor example the length of time it has been in its present location) inresponse to an inquiry.

In yet another embodiment, the present invention can be employed as asystem for controlling and locating inventory, especially retail itemssuch as clothing. In many retail establishments, items for sale arealready tagged with antipilferage devices. The tag elements of thepresent invention can be substituted for such antipilferage devices topermit not only protection from theft but also a capability forelectronic inventory-taking and ready location of objects withparticular attributes, e.g., specific colors, styles, or sizes of suchitems.

For example, clothing stores can employ the present invention to tagarticles of merchandise according to a code that specifies at leastattribute of the clothing or accessory item. When the customer requestsan item in a different color or size, the tore clerk need only activatethe search beacon to generate an interrogation signal and determinewhether such an item having the coded characteristic is in stock. If theitem is in stock, the search signal can simultaneously or subsequentlyactivate an audible sound generator associated with, or incorporatedinto the tag, to permit rapid retrieval. Moreover, the system can beused in a census taking mode on a daily basis to check inventory againstsale and alert the management to items that missing but unaccounted foras sales.

In another aspect of the invention, the tags can be constructed astransponders designed to receive a broadcasted interrogation signaleither within a region or throughout a controlled system. The tag can be“tuned” to a search request or can further include means for comparingthe transmitted search request with its own identification code and, ifa match is determined, a responsive signal is generated by the tag toannounce the location of the item.

In yet another aspect of the invention, the tag elements can be passivetransducers, or powered by an alternative energy source such as a solarcell or a motion-activated dynamo to provide a source of electricalpower which is largely or completely independent of conventionalbatteries. Such power sources can be used to generate a responsiveelectromagnetic signal or trigger an audible signal and thereby aid inmanual location and retrieval of the tagged object.

The invention will next be described in connection with certainpreferred embodiments. However, it should be clear that various changesand modifications can be made by those skilled in the art withoutdeparting from the spirit and scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and objects of the presentinvention, reference should be made to the following detaileddescription and the accompanying drawings, in which:

FIG. 1 is a schematic illustration of an electronic locating systemaccording to the invention employing a plurality of distributedinterrogation and detector elements;

FIG. 2 is a schematic illustration of another embodiment of anelectronic locating system according to the invention employing a singleinterrogation element to search a plurality of regions;

FIG. 3 is an illustration of another embodiment of the present inventionin which the invention is employed to locate and/or inventory officefiles;

FIG. 4 is an illustration of yet another embodiment of the presentinvention in which the invention is employed to locate and/or inventoryretail merchandise;

FIG. 5 is a more detailed schematic illustration of an interrogatingradio frequency transmitter for use in the present invention;

FIG. 6 is a schematic diagram of a tuned circuit for use as a passivetag;

FIG. 6A is a further illustration of the construction of one embodimentof a tuned circuit tag of FIG. 6;

FIG. 7 is a schematic illustration of a receiver for use in the presentinvention;

FIGS. 8A-8D are graphs illustrating an RF interrogation scheme. FIG. 8Ais a graph showing the amplitude of a frequency-swept interrogationsignal over time, while FIG. 8B is a graph of the modulation frequency.FIG. 8C shows the effect of a tag element on the interrogation waveform,as sensed by a receiver near the tag. FIG. 8D is a similar graph showingthe effect of a tag element with different resonant characteristics onthe interrogation waveform, as sensed by a nearby receiver.

FIG. 9 is a schematic illustration of an active transponding tag elementand an associated interrogating transceiver;

FIG. 10 is a schematic illustration of a piezoelectric transponding tagelement;

FIG. 11 is a schematic illustration of another alternative electroniclocating system according to the invention employing a magnetic field asan interrogation signal;

FIG. 12 is a flow diagram of a basic retrieval protocol according to theinvention; and

FIG. 13 is a schematic diagram of a voice recognition system for use inthe present invention.

DETAILED DESCRIPTION

FIG. 1 shows a system 10 for locating objects within a plurality ofinterrogation regions A, B, C . . . N, comprising a controller 12, a setof interrogating transmitters 14A, 14B, 14C . . . 14N, and acomplementary set of receivers 18A . . . 18N. As illustrated, thetransmitters and receivers are coupled to the controller 12 bytransmitter bus 13 and receiver bus 17. In system 10, the controller 12is typically activated by a request for an item, e.g., a request for thelocation of a file or shipment, and causes an interrogation signal 16 tobe transmitted by at least one of the transmitters 14A . . . 14N.Various tagged objects 20 . . . 28 will be subjected to theinterrogation signal 16, but only object—the one requested by theuser—will respond to the interrogation signal. In the illustration ofFIG. 1, object 26 is the object being sought and interrogation signal 16triggers a responsive signal 30 by object 26 which identifies itslocation. This responsive signal 30 is detected by receiver 18C and thelocation of object 26 can then be reported, e.g., via receiver bus 17,to the controller 12. (It should be appreciated that various othercommunication paths or buses can also be incorporated into the system 10to facilitate, for example, user inquiries, automatic reports ontransfers or movements of objects, census taking, etc. Moreover, the“buses” need not be hard-wired electrical circuits but can, instead, beradio transmissions or the like.)

In FIG. 2 an alternative system 10A for locating objects within aplurality of interrogation regions A, B, C . . . N, is shown comprisinga controller 12, a single interrogating transmitter 14, and a set ofreceivers 18A . . . 18N. As illustrated, the plurality of receivers arecoupled to the controller 12 by receiver bus 17. In system 10A, thecontroller 12 is typically activated by a request for an item, e.g., arequest for the location of a file or shipment, and causes aninterrogation signal 16A to be broadcast transmitted by transmitter 14.Various tagged objects 20 . . . 28 again will be subjected to theinterrogation signal 16A, but only object—the one requested by theuser—will respond to the interrogation signal. In the illustration ofFIG. 2, object 26 is again the object being sought and interrogationsignal 16A triggers a responsive signal 30 by object 26 which identifiesits location. This responsive signal 30 is detected by receiver 18C andthe location of object 26 can then be reported, e.g., via receiver bus17, to the controller 12.

In FIG. 3, the present invention is illustrated in the context of anoffice environment. As shown, both the transmitter 14 and the receiver18 are incorporated into a single, wall-mounted, unit 19. Transmitter14, upon activation by a controller, transmits an interrogation signal16 which serves as a search beacon for the entire office. Various files20, 22, 24, and 26 are physically present within the interrogation zonedefined by the transmitted signal 16, but only one file 26 has a tagthat is responsive to the interrogation signal 16. File 26 responds tothe interrogation signal 16 by emitting a responsive signal 30 which isthen detected by the receiver 18. (The tag on file 26 can furtherinclude an audible signal generator which would alert the occupant ofthe office that a location inquiry for that particular file has beenmade by another.)

FIG. 4 shows another embodiment of the present invention in the contextof a merchandise retail store in which an article of clothing of aparticular type, size or style is sought for a customer. As shown, boththe transmitter 14 and the receiver 18 can again be formed into a singleunit 19 (which can also include the controller), that preferably islocated close to the cash register or incorporated into a computerterminal at the check-out counter. As shown in FIG. 4, transceiver unit19 is incorporated into a computer terminal 12A, including a display 11and a keyboard user interface 15. Transmitter 14, upon a locationrequest, transmits an interrogation signal 16 which serves as a searchbeacon for a region of (or the entire) store. Various articles arephysically present within the interrogation zone defined by thetransmitted signal 16, but only one article 26 has a tag that isresponsive to the interrogation signal 16. Article 26 responses to theinterrogation signal 16 by emitting a responsive signal 30 which in thisinstance can be simply an audible signal that is then used by the storeemployee or the customer to locate the article of merchandise.

(Although illustrated in the context of clothing apparel, it should beclear that the invention can likewise be applied to other retailapplications, such as record and compact disc sales, video tape rentals,etc., as well as other commercial businesses, such as stockrooms, mailorder houses, shipping and freight handling operations. The inventioncan also be used in libraries and governmental record depositories.)

FIG. 5 is a schematic illustration of one transmitter 50 useful inconnection with the present invention to generate an interrogationsignal. Transmitter 50 includes a power source 52, a voltage controlledoscillator 54, a radio frequency converter 56 and antenna 58. Thetransmitter can further optionally include a sweep generator 53 and/or asignal coder/modulator 57. In use, the transmitter 50 generates atime-varying electromagnetic signal, the frequency of which isdetermined by the oscillator 54 and converter 56.

In some applications it is sufficient for the transmitter 50 to generatea simple sinusoidal waveform for interrogation purposes. Theinterrogation signal be transmitted at a radio broadcast frequencyranging from about 10 kHz to about 1000 MHz, or at a microwave frequencyin the range from about 1000 MHz to about 2200 MHz. These ranges areparticularly useful in the United States because the U.S. FederalCommunications Commission (“FCC”) has allocated various frequencieswithin these bands of electromagnetic radiation for use in low power,communications and remote control applications without need forlicensure. Frequencies allocated by the FCC for industrial, scientificand medical purposes, which may be useful in implementing the presentinvention, include the 5 MHz, 13.5 MHz, 27 MHz, 40 MHz, 49 MHz, 132 MHzand 905 MHz bands. In one embodiment, the invention can be implementedwith signal coder 57 using one or more of the specific frequenciesallocated by the FCC within the 49 MHz band (49.830, 49.845, 49.860,49.875, 49.890 MHz) which support and permit digitally encodedtransmissions. Alternatively, digital signal transmissions within the900 MHz band can be generated by coder 57. Various other frequencies canalso be employed in accordance with FCC and other regulations.

Various modulation schemes can be used to encode the interrogationsignal, including, for example, amplitude modulation, frequencymodulation, phase modulation, pulse coded modulation and pulse durationmodulation. In another embodiment, the interrogation signal can employ alinear FM “chirped” waveform in conjunction with a matched filter in thereceiver to improve resolution. Alternatively, “Barker” phase codingtechniques can be used. These approaches are particularly useful whenthe tag includes a active receiver component, as discussed in moredetail below.

FIG. 6 is a schematic illustration of a simple tuned circuit 60 whichcan be employed as a passive tag element to respond to anelectromagnetic signal. Circuit 60 comprises an inductance L and acapacitance C in a parallel, resonant-tank configuration. By appropriatechoice of the inductance and capacitance values, the tuned circuit 60 isdesigned to respond only to electromagnetic radiation at a particularfrequency. At the “resonant frequency,” the circuit 60 will absorb aportion of the energy in an interrogation signal, converting the energyinto a current flowing in the circuit 60. The energy is then dissipatedby the tank circuit as a re-radiated, secondary or responsiveelectromagnetic signal. A simple embodiment of tank circuit 60 is shownin FIG. 6A in which circuit 60 is formed by a spiral wound inductivecoil 62 and a conventional capacitor 64. (Various other fabricationtechniques can be employed to create the tank circuit. For example, thecircuit 60 can be formed by etched foil techniques with an etched spiralpattern serving as the inductor and a pair of conductive surfacesseparated by an insulator serving as the capacitor.)

Referring back to FIG. 5, if an interrogation signal 16 is transmittedby transmitter 50, the electromagnetic energy in such signal willinteract with various objects in a predefined zone. In particular,interrogation signals at certain frequencies will excite resonantcircuits which are tuned to such frequencies. Tags which incorporatesuch resonant circuits will respond to an interrogating modulationpattern by resonating at a characteristic rate and such resonantcondition can be detected by a gated detector in a receiver. Otherresonant circuits with different characteristics will either not respondat all or respond with a different “signature.”

For example, the transmitter 50 of FIG. 5 can employ a frequencysweeping generator 53 such that only a portion of the signal is absorbedby the circuit. A time varying matched filter or filter bank can beemployed in a receiver to detect the presence of a particular objectbased on its absorption profile.

In FIG. 7, an illustrative receiver 70 is shown schematically. Receiver70 can include an antenna 72, an amplifier/filter module 74,analog-to-digital thresholding circuitry 76 and a signature-recognizingdigital processor 78. The antenna 72 serves to collect eitherelectromagnetic echoes from a transmitter and/or re-emitted radiation(e.g., resonant frequency radiation) from a tag element, as discussedabove. The collected signals are then amplified and/or filtered by theamplifier/filter module to suppress the broad band—orinterrogation—signal and isolate the responsive signal from the tag'sresonant circuit. The receiver 70 can further include ananalog-to-digital converter assembly 76 which converts the analogsignals from the amplifier/filter module 74 into digital representationsof the response from each tag that has been excited within theinterrogation region. These digital representations are then processedby a computer or other microprocessor to identify or inventory fileswithin an interrogated region.

A detection scheme based on frequency modulation is illustratedschematically in FIGS. 8A-8D. These figures illustrate an RFinterrogation scheme (although they are also applicable to analogousmagnetic field interrogation schemes). FIG. 8A is a graph showing theamplitude of a frequency-swept interrogation signal over time, which canbe generated for example by the transmitter of FIG. 5, while FIG. 8B isa graph of the modulation frequency (curve 73). FIG. 8C shows the effectof a first tag element on the interrogation waveform, as sensed by areceiver near the tag. In this illustration the tag element resonates atparticular frequency which is generated by the transmitter twice duringeach sweep cycle, i.e. at points 71 and 71′ as shown in FIG. 8A. Theseresonance points cause perturbations 77 and 79, respectively in thereceived signal. FIG. 8D is a similar graph showing the effect of asecond tag element with different resonant characteristics on theinterrogation waveform, as sensed by a nearby receiver. It is apparentthat the two tags illustrated in FIGS. 8C and 8D have distinctlydifferent signatures, defined by the timing of their signalperturbations (x and x′ in the case of the first tag, versus y and y′ inthe case of the second tag). By determining the time delays Δ₁ and Δ₂,for each tag, the presence (or absence) of a particular tag within theinterrogation zone can be readily determined. (It should also be clearthat additional modulation patterns or more complex signals, e.g.,quadrature phase shifting or the like, can also be used to furtherfacilitate differentiation of tag elements.)

A more complex system 90, as illustrated in FIG. 9, employs apseudo-random digital coding scheme in an interrogating transceiver 80and/or in a similar coded transponder tag 26A. In this embodiment, thetransceiver 80 includes a front-end transmitter 50 which generates adigitally encoded signal. The signal can be chosen to facilitate aresponse from only one uniquely coded tag element or the interrogationsignal can be a general census call, triggering a response from all tagswithin the interrogation zone. The receiver component 70 of thetransceiver can include a coded signal detector which senses thetransponder signal and correlates it with a stored code to identify thetag (or tags) present in the interrogation zone.

The tag of FIG. 9 can be either passive or active. In the passive mode,the tag circuitry simply accumulates and then returns a signal, if theinterrogation signal matches a predefined code sequence stored in thetag's circuitry. In an active mode the tag element further includes abattery or similar source of power, e.g. a solar cell, which assists insignal amplification, detection and/or waveforming. As shown in FIG. 9,the tag transponder 26 can include receiver circuitry 91, optional powersupply 92, a rectifier/detector and waveformer 93, a comparator (withassociated code memory) 95, a modulator/encoder 94 and a transmitter 96.In use, an interrogation signal is received by the receiver module 91and decoded by detector module 93. The detector generates a waveformwhich can be returned to the interrogating transceiver 80 viatransmitter 96, if the encoded interrogation signal correlates with asequence stored in the code memory 95.

In FIG. 10 a system 100 based on a piezoelectric delay line is shown. Apulse electromagnetic interrogation signal 101 is employed together witha piezoelectric crystal 102 or the like which responds with an echo ifthe pulses are transmitted at a frequency that matches at least one ofthe crystal's resonant characteristics. The echo 103 can be detected bya simple receiver (or an integrated transceiver). The piezoelectriccrystal has an end face that determines the round trip transit time(e.g., based on the length l of the crystal 102). This system 100 isparticularly useful in passive tag structures.

In FIG. 11 yet another system for locating objects is shown based on aoscillating magnetic field and the magnetic tags which are constructedto perturb the oscillation at a specific frequency. In the illustratedembodiment, the system 105 includes an oscillating magnetic fieldgenerator 106 which provides a magnetic field of variable frequencywithin an interrogation region, and at least one tag element 26B whichcomprises a magnetostrictive structure formed, for example, offerromagnetic material and magnetically biased such that it willmechanically resonate at a predefined frequency within the variablefrequency band of the interrogating field generator 106. When themagnetostrictive material resonates, this will perturb the field sensedeither on the coil 107 of field generator 106 or on a second pick-upcoil 108. (The interrogation and detection scheme described above inconnection with RF interrogation can also be used for magnetic tagshaving analogous signature characteristics.) FIG. 12 illustrates aprocess for locating objects which can be used in the present invention.In this system 110, an initial step 112 is taken when the user inputsthe identifier for the item-to-be-located. This can be done by keyboardentry, other touch sensitive mechanisms or by voice. In the next step114, the system can acknowledge the search request either by a displayedor voiced response indicating that the identifier is recognized. In step116, the user can then confirm that the identifier is indeed theidentifier for the item which needs to be located. In step 118, thesystem can read the code for the item from memory, and in step 120 acoded interrogation signal is transmitted to one or more interrogationregions. In step 122, the coded interrogation signal triggers a responseby the item tag and in step 124 a detector within the region senses aresponse. Finally, in step 126, the detector transmits a signal to thesystem (which can be displayed or otherwise communicated, e.g. by voice,to the user) to report the location of the item.

It should be appreciated that various modifications can be made to thebasic system reported above. For example, the system (or amicroprocessor-based controller) can initiate periodic census-taking andstore such data in memory. An inquiry can initially be met withinformation about the last known location of the item. Alternatively,the system simply can interrogate the last known location and, if theitem is found there, report back to the user without any need to pollother locations. Moreover, the system can be used to simply sort outclasses of items and ensure that there are no misplaced items within aparticular interrogation zone (e.g., California-bound luggage in thecargo hold of a Europe-destined flight).

In FIG. 13, a system is shown for voice recognition of inquiries andother instructions in accordance with the present invention. Speechrecognition systems typically operate by matching an acoustic word modelwith an acoustic signal generated by an utterance of the word to berecognized. In many such systems, the acoustic signal generated by aspeaker is converted by an A/D converter into a digital representationof the successive amplitudes of the audio signal created by the speech.The resulting signal is transformed into a frequency domain signal whichconsists of a sequence of frames, each of which provides the amplitudeof the speech signal across a spectrum of frequency bands. Such systemscommonly operate by comparing the sequence of frames produced by theutterance to be recognized with a sequence of nodes, or frame models, aspostulated in the acoustic model of each word in their vocabulary.

Since the individual sounds which make up a given word are seldom spokenat exactly the same relative rate or in exactly the same manner in anytwo utterances of that word, techniques have been developed in the priorart which have greatly improved the performance of speech recognitionsystems. The first is probabilistic matching, which determines thelikelihood that a given frame of an utterance corresponds to a givennode in an acoustic word model. It determines this likelihood not onlyas a function of how closely the amplitudes of the individual frequencybands of the frame match the expected frequencies contained in the givennodes, but also as a function of how the deviation between the actualand expected amplitudes compares to the expected deviations for suchvalues. Such probabilistic matching gives a recognition system a muchgreater ability to deal with the variations in speech sound which occurin different utterances of the same word, as well as a greater abilityto deal with the noise which is commonly present during speechrecognition tasks.

The second major technique which can improve the performance of suchframe matching systems is dynamic programming. In essence, dynamicprogramming provides a method to find an optimal or near optimal matchbetween the sequence of frames produced by an utterance and the sequenceof nodes contained in the model of a word. It does this by effectivelyexpanding and contracting the duration of each node in the acousticmodel of a word to compensate for the natural variations in the durationof speech sounds which occur in different utterances of the same word.Both probabilistic matching and dynamic programming are well known inthe art and software-driven systems which provide highly efficientspeech recognition based upon these and other principles are availablefrom a number of commercial sources including for example, DragonSystems, Inc. of Newton, Mass. In the present invention, suchspeech-recognition systems can be advantageously employed to furthersimplify the task of locating and/or retrieving items. Voice-activatedsystems are particularly useful in applications where keyboard entry oflocation requests is awkward or undesirable.

Referring now to FIG. 13, a schematic block diagram is shown of thehardware used in a speech recognizing embodiment of the invention. Thissystem includes speech processing means 143 for detecting the utteranceof a spoken word and for converting that utterance into digital signalsto which a computer can respond. These means include a microphone 141,an A/D converter 142, a peak-amplitude detector 144, afast-Fourier-transform (or “FFT”) circuit 146, and an utterance detector148. The signals produced by these means are supplied to a programmablecomputer 150, such as, for example, an Intel® processor-based, personalcomputer. In one embodiment, the system acknowledges search requestsorally, e.g., by confirming with a synthetic spoken reply. The computeris provided with a video monitor (not shown) to display words recognizedby it, and a keyboard (not shown), to enable an operator to communicatewith the computer by means other than voice. The monitor, the keyboard,and their respective interfaces to the computer 150, can be of a typecommonly used with personal computers. Alternatively, the microphone,display and/or keyboard functions can be integrated into a desktelephone apparatus under the control of a similar microprocessor eitherhoused within the telephone apparatus or centrally located and connectedto plurality of telephones by an intraoffice telephone link or network.

The output of the microphone 141 is connected to the input of the A/Dconverter 142. The A/D converter converts the analog signal produced bythe microphone 141 into a sequence of digital values representing theamplitude of the signal produced by the microphone 141 at a sequence ofevenly spaced times. For example, the A/D converter 142 can be afourteen-bit converter with a sampling rate of 6000 hertz. The output ofthe A/D converter 142 is supplied to the inputs of the peak-amplitudedetector 144 and the FFT circuit 146.

FFT circuitry is well known in the art of digital signal processing.Such circuitry converts a time domain signal, which gives the amplitudeof a given signal over a succession of times, into a frequency domainsignal, which gives the amplitudes of the given signal at each of aplurality of frequency bands during each of a succession of timeperiods. In the preferred embodiment, the FFT circuit 146 converts theoutput of the A/D converter 142 into a sequence of frames, each of whichindicates the amplitude of the signal supplied by the A/D converter ineach of eight different frequency bands. In one embodiment, FFT circuit146 can produce one such frame every 50th of a second.

As is well known in the art of digital signal processing, the output ofFFT circuitry is generally improved if it includes means for properlywindowing the sequence of amplitude values which is fed to it for thecalculation of each frame. Such windowing tapers values near thebeginning and end of the sequence used for the computation of a givenframe, thus reducing the effect of discontinuities at the boundaries ofthe sample period upon the Fourier transform produced by the FFTcircuit. In the preferred embodiment the FFT circuit 146 uses a type ofwindowing function known in the art as a Hamming window.

The FFT circuit 146 can produce, for example, a vector of valuescorresponding to the energy amplitude in each of eight frequency bands.The FFT circuitry 146 converts each of these eight energy amplitudevalues into an eight-bit logarithmic value. This reduces subsequentcomputation since the eight-bit logarithmic values are more simple toperform calculations on than the longer linear energy amplitude valuesproduced by the fast Fourier transform, but represent the same dynamicrange. Ways for providing logarithmic conversions are well known in theart, one of the simplest being to use a look-up table in memory. Othermodifications of the FFT process, such as averaging and normalization,can also be employed to simplify the speech signal.

The FFT circuit 146 produces an output of one frame every fiftieth of asecond. This output is supplied via bus 160 of the computer 150. The FFTcircuit 146 also supplies an interrupt signal on an output line which isconnected through the system bus 160 to the CPU 164 of the computer 150.In response to the interrupt produced by the FFT circuitry, CPU 164reads the data provided for each successive frame and stores it in arandom access memory 156. The FFT circuitry 146 also supplies frameclock signals to the peak amplitude detector 144 and the utterancedetector 148.

The peak-amplitude detector 144 includes circuitry of a type well knownto those skilled in the digital arts, for storing the highest amplitudevalue produced by the output of the A/D converter 142 during each frametime indicated by the frame clock signal from the FFT circuit 146.

The utterance detector 148 can further include a comparator forcomparing the peak amplitude of the output of and A/D converter 142during a given frame, as determined by the peak-amplitude detector 144,with a predetermined threshold value supplied to a second input of thatcomparator. In one preferred embodiment this threshold is set to a valueapproximately four times higher than that associated with normalbackground sound. It is set to this value by computer 150 over lineswhich are not shown in the figures. During any frame period in which thepeak amplitude exceeds the given threshold, the output of the comparatorproduces a high value.

The computer 150 can be any one of a great number of types of computer,since most general purpose computers can be programmed to function in asimilar manner, provided they have sufficient memory and sufficientcomputational power. The likelihood processor 178 can be implemented byvarious means. See, for example, the discussions of likelihoodprocessors contained in U.S. Pat. No. 4,783,803, the disclosures ofwhich are incorporated herein by reference.

As will be clear to those skilled in the computer arts the decision asto what computational elements of the present invention should beperformed with special-purpose hardware and which should be performed insoftware will depend upon the exact function and market which the systemis designed to fill, and that decision will vary over time as the size,capability, and cost of hardware change. Thus for example, it should beunderstood that a high percent of the computational tasks performed bythe present invention could be performed in special-purpose hardware, aswell as in software, and that many of the tasks which are performed inhardware in the preferred embodiment described here could be performedin software, if desired.

As is described above, the FFT circuit 146 converts the sound occurringin a given twenty millisecond period into a frame which indicates theenergy amplitude in each of several (e.g., eight) spectral bands duringthat period. This frame can be represented as a vector of eightamplitude parameters. Each of the eight parameters actually correspondsto a logarithm of its corresponding energy amplitude value.

In the probabilistic frame matching method used in one preferredembodiment of the present invention, each frame produced by an utteranceis matched against a succession of frame-like nodes contained in themodel of each word of an active vocabulary. Each node has a separateprobability distribution associated with each of the eight parameters ofa frame. Each of the probability distributions associated with a givenparameter has a mean value, μ, which indicates a statistically derivedexpectation of the most probable value for the corresponding frameparameter during a given utterance of that node. In addition, each nodecontains for each frame parameter a σ, which is a statistically derivedindication of the likely deviation of the value of that given frameparameter from the expected value, μ, during the utterance of the node.

The μ and σ car for each parameter of each node in a word model can bederived by statistical techniques. For example a plurality of utterancesof a given word can be divided into a plurality of nodes by a humanlistener playing back a recording of each word at a slow pace. Then thevalue of μ and σ can be calculated for each node by standard statisticaltechniques. More efficient automatic methods of deriving node models arealso available.

The computational structure of likelihood processor 178 typicallyinvolves two major sequential components which are performed after theutterance of a word has been detected. First a rapid match computationis performed to derive from an initial vocabulary a smaller, originallyactive, vocabulary containing the words which appear to have areasonable chance of matching the detected utterance. Then, after therapid match computation, a more lengthy and accurate word matchcomputation is performed upon each of the words in the originally activevocabulary. The application of speech recognizing techniques asdescribed above to electronic location systems is facilitated by thelimited active vocabulary that is needed to fulfill a search request.Typically, the user simply utters an ID number associated with theobject, e.g. “Find File TJE-001.” Next, the computer the recognizes therequest, confirms it by repeating the best match (as determined by thelikelihood processor) and then executes the instruction by signaling thecontroller to begin a search of the various interrogation zones.

Computer 150 is connected via bus 170 to controller 12 which includes auser interface 172 (e.g., a video display and/or a synthetic speechgenerator and speaker in order to confirm the search request) and asearch processor 174, which generates interrogation signals and decodestag responses, as discussed above. Data on the location of items fromeither a specific search request or periodic census-taking can be storedin location memory 176.

1. A system for locating an object comprising: at least one transmitterfor transmitting of an electromagnetic interrogation signal within eachof a plurality of defined interrogation zones; at least one tag adaptedfor attachment to an object, the tag being responsive to saidelectromagnetic interrogation signal and comprising a signal receivingstructure adapted to capture at least a portion of the energy of saidinterrogation signal, and a response generator for generating aresponsive signal to announce the presence of the object within aninterrogation zone; a plurality of receivers, each associated with oneof the interrogation zones for detecting said responsive signal fromsaid tag, if present, within its interrogation zone; a controller forperiodically activating the at least one transmitter to conduct a censusof tagged objects within the interrogation zones; a data storage devicefor recording the results of the census as a location inventory thatidentifies tagged objects as present in one of said interrogation zones;and a search processor that responds to a user initiated search forspecific tagged object by first checking the data storage device for alast known location of the object in the location inventory andactivating at least one of the transmitters to confirm and update thelocation of the tagged object based on a responsive signal from areceiver associated with the zone in which the object is located.
 2. Thesystem of claim 1 wherein the transmitter further comprises a modulatorthat varies the frequency of signals generated by an electromagneticradiation signal generator in accordance with a control signal from thecontroller.
 3. The system of claim 1 wherein signal receiving structurefurther comprises a tank circuit tuned to a frequency of theelectromagnetic signal.
 4. The system of claim 1 wherein signalreceiving structure further comprises a piezoelectric crystaltransponder.
 5. The system of claim 1 wherein signal receiving structurefurther comprises a magnetorestrictive element.
 6. The system of claim 1wherein the transmitter further comprises a digital code generator thatencodes an electromagnetic radiation signal in accordance with a controlsignal from the controller.
 7. The system of claim 1 wherein thetransmitter generates a coded interrogation signal addressed to aspecific tag ID.
 8. The system of claim 1 wherein the system furthercomprises a user interface for entering requests for location ofparticular tagged objects.
 9. The system of claim 8 wherein the userinterface is incorporated into a computer terminal.
 10. The system ofclaim 1 wherein the system further comprises a display for displayinginformation on a tagged object.
 11. The system of claim 1 wherein thesystem further comprises a plurality of transmitters for interrogatingdifferent locations.
 12. The system of claim 11 wherein the data storagedevice is adapted to store information on tagged objects in theplurality of locations.
 13. The system of claim 12 wherein the systemfurther comprises a user interface.